Flexible endoscopic evaluation of swallowing (FEES) has been available, since approximately 1988, to assess patient swallowing function and determine appropriate oral intake. At this stage, FEES is not a novel diagnostic tool;however, what is novel are the findings from our pilot data on swallowing as assessed in healthy participants. Surprisingly, scant data exist on "normal swallowing" to guide health care providers in determining what constitutes "abnormal swallowing." In our pilot studies, we found an unexpectedly broad range of normal swallowing that has not been previously reported or currently appreciated. That is, we found in 65 healthy older adult participants, slower swallowing than expected, food and liquid residue in their throats, and occurrences of aspiration (i.e., food or liquid enters the airway below the level of the vocal folds). Specifically, on the latter observation, we found that 19% of our older adults demonstrated aspiration at some point and time during the pilot studies. Accordingly, the primary aim of this project is to examine swallowing, via FEES, in normal participants across the life span in an effort to provide an accurate definition of normal to serve as a benchmark for the diagnoses of abnormal swallowing in both clinical and research realms. Specific aim one is to assess the effect of age, gender, bolus type, bolus volume, bolus viscosity, and bolus delivery method on swallowing in healthy participants. Swallowing will be assessed with four indices: 1) penetration aspiration scale (PAS) scores, 2) pharyngeal response duration, 3) pharyngeal closure duration, and 4) pharyngeal residue during FEES. Two hundred ten individuals, 20-90 years old will participate. Our pilot data support the following hypotheses: More penetration and aspiration events, longer pharyngeal response, longer pharyngeal closure duration, and greater residue are observed in older adults. Pharyngeal closure duration is longer in males than in females. Penetration and aspiration occurrences are greater, pharyngeal response times are longer, and pharyngeal residue is greater with larger boluses. Penetration and aspiration events/scores are affected by bolus type (e.g., milk vs. water) and viscosity (e.g., thin liquid vs. puree). Four experiments are proposed to further investigate these preliminary findings in detail. Specific aim two is to determine the intra-and inter-rater reliability of the four swallowing parameters. Intra-rater reliability will be tabulated from nine clinicians as a function of initial, and short- (i.e., one day) and long-term (i.e., one-week) repeat ratings. Inter-rater reliability will be acquired as a function of clinician endoscopic experience from nine clinicians of equal balanced groups (i.e., beginning, intermediate, and advanced = 10-100, 101-1,000, and 1,001-10,000 FEES performed, respectively). Completing these two aims will provide robust preliminary data on swallowing in normal participants and its reliability as assessed with FEES. The results of this exploratory R03 pilot grant will guide the stratification needs of a R01 grant platform that will obtain extensive normative data on swallowing with FEES. Relevance: The primary aim of this project is to examine swallowing, via Flexible Endoscopic Evaluation of Swallowing (FEES), in healthy participants across the life span. Currently, there is surprisingly little data on normal swallowing for clinicians and researchers to accurately diagnose swallowing disorders and make appropriate diet recommendations. The information derived from this study will not only serve to greatly enhance diagnosis and clinical care of patients with swallowing disorders but also serve as foundational data on normal swallowing of which to build a R01 grant application.